Food cooking apparatus and temperature control method thereof

Abstract

The application provides a food cooking device and a temperature control method thereof. The device comprises a chamber for accommodating food to be cooked, a plurality of heating elements arranged corresponding to the chamber, a plurality of switching elements respectively connected to the plurality of heating elements to adjust the output of the plurality of heating elements in a duty cycle manner, and a temperature sensing element for detecting the actual temperature in the chamber. The controller is configured to set a target temperature of the chamber. The food cooking device further comprises a controller configured to perform: a total duty cycle calculation step of calculating a total duty cycle according to the actual temperature and the target temperature; and a duty cycle determination step of determining the duty cycle corresponding to each switching element according to the total duty cycle and a preset proportional relationship. The application can meet the temperature distribution requirements of different areas in the chamber, improve the accuracy of temperature control, and save costs.

Description

Technical Field

[0001] This invention relates to the field of household appliance technology, specifically to a food preparation device and its temperature control method. Background Technology

[0002] Existing food processing devices typically use sensors to measure the temperature of the food processing chamber and then use switching elements to control the heating element based on the measured temperature. For example, the heating element is turned off when the sensor temperature reaches or exceeds the target temperature, and turned on when the temperature falls below the target temperature, thereby achieving the purpose of controlling the temperature of the food processing device.

[0003] However, due to differences in the type, specifications, types of food processed, and external environment of various food processing devices, even with the above adjustments, the overall temperature fluctuation of the chamber may be large, or the temperature variation at different locations within the same chamber may differ, leading to inaccurate temperature control and affecting the quality of food processing. Therefore, a technical solution is urgently needed to improve the accuracy of temperature control. Summary of the Invention

[0004] To address the above problems, this invention provides a food preparation device and its temperature control method. By calculating the total duty cycle and distributing it proportionally to multiple switching elements, the operation of the heating element is controlled. This satisfies the temperature distribution requirements of different areas within the chamber, improves the accuracy of temperature control, and optimizes the temperature control of the food preparation device without increasing hardware costs. This saves costs and enhances the temperature control capability of the food preparation device, meeting higher requirements for food preparation.

[0005] This invention provides a food preparation device, comprising: a chamber for containing food to be prepared; multiple heating elements disposed corresponding to the chamber and used to heat the chamber; multiple switching elements connected to the multiple heating elements respectively, adjusting the output of the multiple heating elements by adjusting the duty cycle; a temperature sensing element for detecting the actual temperature inside the chamber; and a controller for setting a target temperature for the chamber. The controller is configured to perform: a total duty cycle calculation step, calculating the total duty cycle based on the actual temperature and the target temperature; and a duty cycle determination step, determining the duty cycle corresponding to each switching element based on the total duty cycle and a preset proportional relationship.

[0006] According to this technical solution, by calculating the total duty cycle and adjusting the switching duration of multiple heating elements according to the duty cycle, the output of heating elements with non-adjustable power can be regulated, thereby regulating the temperature inside the chamber. By distributing the total duty cycle to multiple heating elements according to a preset relationship, the temperature distribution requirements of different areas inside the chamber can be met, improving the accuracy of temperature control. Furthermore, it avoids the problem of excessively high local temperatures caused by using only a single heating element, which could lead to irreversible discoloration, degradation, or other damage to the chamber materials. By having the controller calculate and determine the duty cycle of each switching element, precise and stable temperature control can be achieved without adding hardware; only the software algorithm needs improvement, balancing cost and temperature regulation effectiveness.

[0007] In the optional technical solution of the present invention, the preset ratio of the duty cycle of each switching element to the total duty cycle is: an = kn * a, where a1, a2...an are the duty cycles of each switching element; a is the total duty cycle; and k1, k2...kn are proportional coefficients.

[0008] According to this technical solution, by proportionally distributing the duty cycle to multiple switching elements to regulate the temperature inside the food cooking device, the temperature variation at different locations is minimized, which improves the temperature uniformity inside the food cooking device and avoids the defect of uneven temperature distribution caused by using a single heating element, thus extending the service life of the food cooking device.

[0009] In the optional technical solution of the present invention, the proportionality coefficient is the dependent variable of the target temperature. Specifically, the proportionality coefficient of the same heating element is different for different target temperatures. By adjusting the proportionality coefficient according to different target temperatures, the temperature distribution within the food preparation device can be improved, thereby enhancing the quality of food preparation.

[0010] In an optional technical solution of the present invention, the controller is further configured to perform: determining whether the difference between the actual temperature and the target temperature is within a specified temperature difference range, and determining whether to perform the total duty cycle calculation step and the duty cycle determination step based on the determination result.

[0011] According to this technical solution, the total duty cycle calculation step and the duty cycle determination step are selectively executed based on whether the difference between the actual temperature and the target temperature is within the specified temperature difference range. This allows for different execution actions to be performed within different specified temperature difference ranges, thereby improving the accuracy of temperature control.

[0012] In the optional technical solution of the present invention, the temperature difference range is defined to include a low temperature zone, a temperature control zone, and a high temperature zone. The temperature range of the temperature control zone is located between the low temperature zone and the high temperature zone. If the difference is in the low temperature zone or the high temperature zone, the total duty cycle calculation step and the duty cycle determination step are skipped. If the difference is in the temperature control zone, the total duty cycle calculation step and the duty cycle determination step are executed.

[0013] According to this technical solution, when the temperature difference is in the high-temperature zone, the heating element is usually turned off or its output is significantly reduced to quickly bring the actual temperature of the food preparation device closer to the target temperature; this is called "fast adjustment." Similarly, when the temperature difference is in the low-temperature zone, the output of the heating element is usually increased to accelerate the attainment of the target temperature; this is also called "fast adjustment." The temperature range of the temperature control zone is closer to the target temperature than the low-temperature and high-temperature zones. When the actual temperature approaches the target temperature, the total duty cycle calculation and duty cycle determination steps are performed, which reduces the step size of each temperature adjustment; this is called "slow adjustment." This overcomes the shortcomings of rapid temperature rise or fall causing large temperature fluctuations within the food preparation device, making it difficult to stabilize at the target temperature for a long time, and resulting in high energy consumption. Furthermore, by finely adjusting the output duty cycle, the temperature gradually converges to the target temperature without increasing the number of switching element operations, ensuring that the lifespan of the switching elements is not reduced.

[0014] In an optional technical solution of the present invention, the controller is further configured to perform: a judgment step, determining whether the temperature zone currently occupied by the actual temperature and the temperature zone previously occupied are respectively a low temperature zone and a high temperature zone, or a high temperature zone and a low temperature zone; if so, it is counted as one switching between the low temperature zone and the high temperature zone; a recording step, recording the number of switching between the low temperature zone and the high temperature zone; a comparison step, comparing the number of switching with the preset number; if the number of switching is not less than the preset number, then performing the total duty cycle calculation step and the duty cycle determination step.

[0015] According to this technical solution, when the temperature difference is in the high-temperature zone, the heating element is usually turned off or its output is significantly reduced to quickly bring the actual temperature of the food preparation device closer to the target temperature. When the temperature difference is in the low-temperature zone, the output of the heating element is usually increased to accelerate the achievement of the target temperature. By determining the number of times the actual temperature switches between the high-temperature and low-temperature zones, a temperature oscillation occurs when the number of switches reaches a preset number. By executing the total duty cycle calculation and duty cycle determination steps, the temperature zone switching is stopped, suppressing the occurrence of temperature oscillation and keeping the food preparation device in a slow temperature control phase. This ensures the stability of the food preparation device's temperature and is also beneficial for energy saving.

[0016] In an optional technical solution of the present invention, the switching element is a relay, and the working cycle of the relay is 10-30s.

[0017] According to this technical solution, the relay mainly relies on the attraction of copper strips to control the on and off states. The shorter the relay's working cycle, the better it is for temperature stability; the longer the cycle, the better it is for ensuring the relay's service life. By referring to the relay's specifications and product life cycle, a cycle of about 20 seconds is more appropriate to prevent the relay's lifespan from being too short, while also having lower energy consumption and lower cost.

[0018] In the optional technical solutions of the present invention, the switching element is a solid-state relay or a thyristor.

[0019] According to this technical solution, solid-state relays mainly rely on semiconductor elements to achieve switching, and can control the switching of heating elements in a short period of time using pulse width modulation (PWM) to meet the needs of temperature regulation. They have better temperature control effect, and solid-state relays can control the power adjustment of adjustable heating elements, making them widely applicable.

[0020] The present invention also provides a temperature control method for a food processing device, the food processing device comprising: a chamber for containing food to be processed; multiple heating elements disposed corresponding to the chamber and used to heat the chamber; multiple switching elements respectively connected to the multiple heating elements to adjust the output of the multiple heating elements by adjusting the duty cycle; a temperature sensing element for detecting the actual temperature inside the chamber; and a controller for setting the target temperature of the chamber. The temperature control method includes the following steps: a total duty cycle calculation step, calculating the total duty cycle based on the actual temperature and the target temperature; and a duty cycle determination step, determining the duty cycle corresponding to each switching element based on the total duty cycle and a preset proportional relationship.

[0021] In the optional technical solution of the present invention, the preset ratio of the duty cycle of each switching element to the total duty cycle is: an = kn * a, where a1, a2...an are the duty cycles of each switching element; a is the total duty cycle; and k1, k2...kn are proportional coefficients. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the modular structure of the food preparation device in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of temperature change curves corresponding to different temperature control methods when the target temperature is low in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of temperature change curves corresponding to different temperature control methods when the target temperature is high in an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram showing the distribution of temperature bands after the actual temperature and the target temperature initially reach consistency in Scheme 2 of the present invention.

[0026] Figure 5 This is a schematic diagram of temperature change curves under voltage fluctuation conditions in an embodiment of the present invention.

[0027] Figure 6 This is a schematic diagram of the temperature control method of the food preparation device in an embodiment of the present invention.

[0028] Figure label:

[0029] Chamber 1; heating element 2; switching element 3; temperature sensing element 4; controller 5. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, this invention provides a food preparation device, including: a chamber 1, multiple heating elements 2, multiple switching elements 3, a temperature sensing element 4, and a controller 5 (preferably a microcontroller MCU). The chamber 1 is used to contain food to be prepared; the multiple heating elements 2 are arranged corresponding to the chamber 1; the multiple switching elements 3 are respectively connected to the multiple heating elements 2 to adjust the output of the multiple heating elements 2 by adjusting the duty cycle; the temperature sensing element 4 is used to detect the actual temperature inside the chamber 1; the controller 5 is used to set the target temperature of the chamber 1; the controller 5 is configured to perform: a total duty cycle calculation step, calculating the total duty cycle based on the actual temperature and the target temperature; and a duty cycle determination step, determining the duty cycle corresponding to each switching element 3 based on the total duty cycle and a preset proportional relationship. It should be noted that... Figure 1 Although all components are shown in the diagram, it does not mean that the heating element 2, the switching element 3, the temperature sensing element 4, the controller 5, etc. are all located in the chamber 1. Usually, the heating element 2 and the temperature sensing element 4 can be set in relation to the chamber 1 to heat the chamber 1 and sense the temperature inside the chamber 1. The switching element 3 and the controller 6 are located inside the housing.

[0032] In this embodiment, by calculating the total duty cycle and adjusting the switching duration of multiple heating elements 2 according to the duty cycle, the output of the heating element 2 with non-adjustable power can be adjusted, thereby regulating the temperature inside the chamber 1. By distributing the total duty cycle to multiple heating elements 2 according to a preset relationship, the temperature distribution requirements of different areas inside the chamber can be met, improving the accuracy of temperature control. It can also avoid the problem of excessively high local temperatures caused by using a single heating element 2, resulting in irreversible discoloration, deformation, and other damage to the chamber material. By having the controller 5 calculate and determine the duty cycle of each heating element 2, no additional hardware facilities are required; only the software algorithm needs to be improved to achieve precise and stable temperature control, balancing cost and temperature regulation effect.

[0033] Specifically, in this embodiment, the total duty cycle is calculated based on a PID algorithm. The PID algorithm can automatically adjust the output total duty cycle according to real-time data of the actual temperature and the target temperature, achieving dynamic adjustment and exhibiting good adaptability. It can adapt to different control requirements in different environments, and after the temperature reaches a steady state, the control accuracy can be improved by fine-tuning the duty cycle, making the food processing device control temperature faster and more accurately. The parameters used in the PID algorithm can be adjusted and selected according to actual experiments. ， It is simple to calculate, easy to implement, and suitable for a wide range of applications.

[0034] The controller 5, serving as the carrier for executing algorithms and steps, is not limited in its specific structural form. Any hardware controller 5 with programmable and computing capabilities can be used. Alternatively, the aforementioned algorithms and steps can be integrated into some hardware facilities of the food preparation device itself. This allows for meeting higher food preparation requirements and improving the accuracy and stability of temperature control of the food preparation device without increasing hardware costs. In addition to executing the steps, methods, and logic block diagrams exemplified in this embodiment, the controller 5 can also receive temperature data from the temperature sensing element 4 and control the opening or closing of the switching element 3, causing each heating element 2 to perform heating or non-heating actions.

[0035] In a preferred embodiment of the present invention, the preset proportional relationship between the duty cycle of each switching element 3 and the total duty cycle is: an = kn * a, where a1, a2…an are the duty cycles of each switching element 3; a is the total duty cycle; and k1, k2…kn are proportionality coefficients. By distributing the duty cycles proportionally to multiple switching elements 3 to regulate the temperature within the food cooking apparatus, the uniformity of temperature within the food cooking apparatus can be improved, and the drawback of using a single specific heating element 2 leading to a shortened lifespan and frequent replacements can be avoided, thus extending the service life of the food cooking apparatus.

[0036] In a preferred embodiment of the present invention, the proportionality coefficient is the dependent variable of the target temperature. Different target temperatures result in different proportionality coefficients for the same heating element 2. By adjusting the proportionality coefficient according to the different target temperatures, the temperature distribution within the food preparation apparatus can be improved, thereby enhancing the quality of the food preparation. In some embodiments, the proportionality coefficient can be determined by treating parameters such as the target temperature, the type of food, and the power range of the heating element 2 as individual variables through numerous experiments. This allows for meeting the diverse food preparation requirements and the cooking temperature needs of different types of heating elements 2. The evaluation of the experimental results can be based on the browning of the food from top to bottom. If the food is browned evenly from top to bottom, the duty cycle or proportionality coefficient of the corresponding heating elements 22, as well as the target temperature, are all optimal parameters. If there is a significant difference in browning between the top and bottom of the food, the duty cycle of the heating element 2 at the corresponding part of the food can be adjusted according to the specific browning situation (e.g., darker browning on the upper surface and lighter browning on the lower surface). This involves decreasing the proportionality coefficient of the duty cycle of the heating element 2 corresponding to the upper surface of the food and increasing the proportionality coefficient of the duty cycle of the heating element 2 corresponding to the lower surface of the food.

[0037] In a preferred embodiment of the present invention, the controller 5 is further configured to: determine whether the difference between the actual temperature and the target temperature is within a specified temperature difference range, and determine whether to execute the total duty cycle calculation step and the duty cycle determination step based on the determination result. Selectively executing the total duty cycle calculation step and the duty cycle determination step based on whether the difference between the actual temperature and the target temperature is within a specified temperature difference range allows for different execution actions corresponding to different specified temperature difference ranges, thereby improving the accuracy of temperature control.

[0038] Specifically, the temperature difference range is defined to include a low-temperature zone, a temperature-controlled zone, and a high-temperature zone. The temperature range of the temperature-controlled zone is between the low-temperature zone and the high-temperature zone. If the difference is in the low-temperature zone or the high-temperature zone, the total duty cycle calculation step and the duty cycle determination step are skipped. If the difference is in the temperature-controlled zone, the total duty cycle calculation step and the duty cycle determination step are executed.

[0039] When the temperature difference is in the high-temperature zone, the heating element 2 is usually turned off or its output is significantly reduced to quickly bring the actual temperature inside the food preparation device to the target temperature. That is, when the temperature difference is in the high-temperature zone, the duty cycle of multiple heating elements 2 can be preset to 0, and the heating elements 2 can be controlled to operate at a 0% duty cycle. When the temperature difference is in the low-temperature zone, to accelerate the reaching of the target temperature, the output of the heating element 2 is usually increased to quickly bring the actual temperature to the target temperature. That is, when the temperature difference is in the low-temperature zone, the duty cycle of multiple heating elements 2 can be preset to 100%, and the multiple heating elements 2 can be controlled to operate at a 100% duty cycle.

[0040] The temperature range of the temperature control zone is closer to the target temperature than that of the low temperature zone and the high temperature zone (e.g., the temperature difference between the actual temperature and the target temperature is ±10℃, ±20℃, etc., and the specific temperature difference range can be adjusted according to the required control accuracy). When the actual temperature is close to the target temperature, the total duty cycle calculation step and the duty cycle determination step are executed. This avoids the simple adjustment method of adjusting the duty cycle of heating element 2 to 0 or 100%. It can reduce the step size of temperature adjustment and overcome the defects of large temperature fluctuations in the food processing device caused by rapid temperature rise or fall, which cannot be stabilized at the target temperature for a long time and has high energy consumption. Furthermore, by reducing the step size of temperature adjustment, the feedback temperature can be made more stable and accurate, thereby obtaining a more stable duty cycle output calculation result and further improving the temperature stability.

[0041] The following explanation uses an oven as an example of a food preparation device. Figure 2 As shown, Existing Technology 1 is a temperature change curve diagram under the condition that the target temperature is 30℃ and the oven is empty, with time on the horizontal axis; Existing Technology 2 is a temperature change curve diagram diagram under the condition that the target temperature is 40℃ and the oven is empty. Scheme 1 is a temperature change curve diagram diagram under the condition that the target temperature is 30℃ and the oven is empty, and the total duty cycle calculation and duty cycle determination steps are performed in the temperature control zone. (As shown...) Figure 3 As shown, Existing Technology 3 is a temperature change curve under the condition that the target temperature is 170℃ and the oven is empty, with time on the horizontal axis; Scheme 2 is a schematic diagram of the temperature change curve under the condition that the target temperature is 170℃ and the oven is empty, and the total duty cycle calculation step and the duty cycle determination step are performed in the temperature control zone.

[0042] As can be seen from the attached figures, compared to existing technologies 1, 2, and 3, which shut off heating element 2 upon reaching the target temperature and turn it on before reaching the target temperature, resulting in larger temperature fluctuations and continuous temperature volatility as the actual temperature approaches the target temperature, the actual temperature in this solution exhibits a relatively flat temperature change curve after reaching the target temperature, without obvious peaks and troughs, demonstrating better temperature stability and improved temperature control accuracy. Figure 4 As shown, the horizontal axis represents the actual temperature, and the vertical axis represents the number of sampling points (the number of times the actual temperature reaches the corresponding temperature shown on the horizontal axis). After the actual temperature reaches the target temperature, the average temperature of this embodiment is 171℃. The probability of the temperature being concentrated between 170-172℃ is 85.6%, and the probability of the actual temperature being concentrated between 170.5-171.5℃ is 60.5%, indicating high temperature stability.

[0043] As can be seen from the accompanying drawings, in this embodiment, the highest temperature during the heating phase (200°C) is lower than the temperature rise of the prior art (around 240°C), and the overshoot in this embodiment (30°C) is smaller than the overshoot of the prior art (70°C). Furthermore, the magnitude of the temperature overshoot can be adjusted according to the characteristics of the application (e.g., in the initial stage of cooking, a rapid temperature increase may be required, and the actual temperature will be set slightly higher than the target temperature). Adjusting the parameters as needed can further reduce the temperature overshoot and improve the energy efficiency of the food preparation device. Figure 3 L1 and L2 represent the time it takes for the actual temperature of Existing Technology 3 and Scheme 2 to reach the target temperature, respectively. Scheme 3 takes a relatively long time to reach the target temperature. Although it takes a little longer to reach the target temperature, its energy efficiency and stability are better.

[0044] Furthermore, as can be seen from the above diagram, different target temperatures require different specified temperature ranges (e.g., different functional stages of the food preparation device). Figure 2 The middle stage is fermentation, and the target temperature is relatively low. Figure 3 (For the baking stage, the target temperature is relatively high.) When the target temperature is 40℃, the ambient temperature is around 20℃. During the fermentation stage, the temperature control strategy is generally implemented directly to avoid temperature runaway caused by large outputs in the low-temperature zone. When the target temperature is 170℃, the absolute value of the temperature difference corresponding to the preset temperature control zone is about 20, 25, and 30℃ (if the temperature difference range is too small, temperature oscillation is likely to occur); in the low-temperature zone, the difference between the actual temperature and the target temperature is less than -40℃, and in the high-temperature zone, the difference between the actual temperature and the target temperature is greater than 40℃.

[0045] In some implementations, transitional temperature zones may exist between the low-temperature zone and the temperature control zone, and between the high-temperature zone and the temperature control zone; that is, the low-temperature zone, the temperature control zone, and the high-temperature zone are not temperature-continuous zones. Specifically, when the target temperature is 170℃, the absolute value of the temperature difference corresponding to the preset temperature control zone can be set to 20℃. In the low-temperature zone, the difference between the actual temperature and the target temperature is set to be less than -40℃, and the range where the difference between the actual temperature and the target temperature is less than -40℃ and greater than or equal to -30℃ is defined as the first transitional temperature zone. In the high-temperature zone, the difference between the actual temperature and the target temperature is set to be greater than 40℃, and the range where the difference between the actual temperature and the target temperature is greater than 30℃ and less than or equal to 40℃ is defined as the second transitional temperature zone. By dividing these transitional temperature zones and setting corresponding duty cycles, the accuracy of temperature control can be improved. Specifically, in the low-temperature zone, multiple heating elements 2 operate with a first duty cycle; in the high-temperature zone, multiple heating elements 2 operate with a second duty cycle; and in the temperature control zone, the total duty cycle of multiple heating elements 2 calculated based on the PID algorithm operates according to a preset relationship.

[0046] In the first transition temperature zone between the temperature control zone and the low temperature zone, multiple heating elements 2 operate with a third duty cycle, which can be slightly smaller than the first duty cycle, to ensure that the oven can still heat up quickly when the temperature inside is low, and can continue to heat up at a relatively slow rate when the temperature is close to the target temperature but not within the temperature control zone, thereby avoiding drastic temperature changes.

[0047] In the second transition temperature zone between the temperature control zone and the high-temperature zone, the heating element 2 operates with a fourth duty cycle. This fourth duty cycle can be slightly larger than the third duty cycle, but both the third and fourth duty cycles are smaller than the first duty cycle. Operating the heating element 2 with corresponding duty cycles in different temperature zones improves the accuracy of temperature control. While this embodiment provides the above example, those skilled in the art can limit the number of transition temperature zones and their duty cycles according to actual conditions to enhance the temperature control capability of the food preparation device.

[0048] In a preferred embodiment of the present invention, the controller 5 is further configured to execute: a judgment step, determining whether the current temperature zone of the actual temperature and the previous temperature zone are respectively a low-temperature zone and a high-temperature zone, or respectively a high-temperature zone and a low-temperature zone; if so, counting it as one switch between the low-temperature zone and the high-temperature zone; a recording step, recording the number of switches between the low-temperature zone and the high-temperature zone of the actual temperature; a comparison step, comparing the number of switches with a preset number; if the number of switches is not less than the preset number, then regardless of whether the difference between the actual temperature and the target temperature is in the low-temperature zone, the temperature-controlled zone, or the high-temperature zone, the total duty cycle calculation step and the duty cycle determination step are executed. Here, the current temperature zone refers to which of the low-temperature zone, the temperature-controlled zone, and the high-temperature zone the difference between the current actual temperature and the target temperature is in, and the previous temperature zone refers to which of the low-temperature zone, the temperature-controlled zone, and the high-temperature zone the difference between the previously measured actual temperature and the target temperature was in.

[0049] In the above manner, when the temperature difference is in the high-temperature zone, the heating element 2 is usually turned off or its output is significantly reduced to quickly bring the actual temperature of the food preparation device closer to the target temperature. When the temperature difference is in the low-temperature zone, the output of the heating element 2 is usually increased to accelerate the achievement of the target temperature. By judging the number of times the actual temperature switches between the high-temperature and low-temperature zones, when the number of switches reaches the preset number, temperature oscillation occurs. By executing the total duty cycle calculation step and the duty cycle determination step, the temperature zone switching is stopped, suppressing the occurrence of temperature oscillation. This keeps the food preparation device in a slow temperature control stage, ensuring the stability of the temperature inside the food preparation device and contributing to energy saving.

[0050] In a preferred embodiment of the present invention, the switching element 3 is a relay, and the relay's operating cycle is 11-22 seconds. The relay primarily controls the switching by the engagement of a copper strip. Controlling the relay's operating cycle to 11-22 seconds ensures its lifespan, preventing excessive switching frequency due to a short cycle, which would reduce the relay's lifespan and fail to meet the lifespan requirements of the food processing device throughout its lifespan. Furthermore, appropriately extending the relay's operating cycle slows down the temperature regulation speed, ensuring temperature stability and preventing excessive temperature fluctuations caused by rapid temperature changes. In addition, the relay has low energy consumption and low cost. Using a relay as the switching element 3 eliminates the need for additional heat dissipation devices (such as heat sinks or cooling fans), further saving costs. It should be noted that the operating cycle referred to in this embodiment is the time required for the relay to go from engaging to disengaging and back to engaging. In some implementations, a reasonable working cycle is set, and the cycle is divided into speed levels at the millisecond, minute, and centisecond levels. Within each working cycle, the on-time of heating element 2 is fine-tuned at the millisecond, minute, and centisecond levels based on the PID calculation value (e.g., if the original on-time of heating element 2 was 1 second, the adjusted on-time can be accurate to 1.1 seconds). This does not increase the number of relay actions and shorten the relay's lifespan, and it achieves precise control of output energy with low hardware costs, thus realizing accurate temperature control.

[0051] In some other embodiments, the switching element 3 is a solid-state relay. Solid-state relays mainly rely on semiconductor elements to achieve switching, and can control the switching of heating element 2 at high frequency within a short cycle to meet the temperature regulation requirements, thus having a better temperature control effect. In addition, solid-state relays can control the power adjustment of the adjustable heating element 2, and have a wide range of applications.

[0052] In some implementations, this implementation can adaptively adjust the total output duty cycle to adjust the actual temperature towards the target temperature in response to temperature changes caused by voltage fluctuations. For example... Figure 5 As shown, when the voltage fluctuates, the center temperature of the food preparation device and the temperature of the temperature sensor drop synchronously, and after a short period of adjustment, they can both return to the target temperature.

[0053] Specifically, at a standard voltage of 220V ( Figure 5 At point A), after the actual temperature reaches the target temperature, the output time required for multiple heating elements 2 to maintain the target temperature within one working cycle is 2.5s / 11s; the voltage drops to 192V. Figure 4 At point B, the actual temperature dropped by nearly 5°C before recovering to near the target temperature. The duty cycle of the outputs of multiple heating elements 2 was 3.1s / 11s. The voltage increased to 242V. Figure 4At point C, the actual temperature rises by nearly 10°C and then recovers to near the target temperature. The required output duty cycle for the multiple heating elements 2 is 2.0s / 11s. In this embodiment, the temperature control scheme can control the temperature to near the target temperature within a short time after a voltage change, and the output time for the actual temperature to recover to near the target temperature is close to the theoretical value.

[0054] In addition, differences between heating elements 2 (power tolerance of heating elements 2) and differences in food preparation devices will also affect the temperature. The temperature control scheme provided in this embodiment can overcome the effects of the above differences, ensure the accuracy of temperature control, and improve the stability of temperature.

[0055] like Figure 5 As shown, the present invention further provides a temperature control method for the above-mentioned food preparation apparatus, comprising the following steps:

[0056] Initialization switching count i = 0;

[0057] Detect the temperature inside the chamber and set the target temperature;

[0058] The comparison step compares whether the number of switching times has reached the preset number. If the preset number has been reached, the control process of the temperature control zone is executed.

[0059] If the preset number of attempts is not reached, controller 5 is also configured to execute:

[0060] The judgment step is to determine whether the current temperature zone and the previous temperature zone are respectively a low temperature zone and a high temperature zone, or a high temperature zone and a low temperature zone.

[0061] If not, when the actual temperature is currently in a high-temperature zone, the total duty cycle calculation step and the duty cycle determination step are skipped, and the heating element 2 is controlled to execute the duty cycle corresponding to the high-temperature zone; when the actual temperature is currently in a low-temperature zone, the total duty cycle calculation step and the duty cycle determination step are skipped, and multiple heating elements 2 are controlled to execute the duty cycle corresponding to the low-temperature zone.

[0062] If so, it is counted as one switch between the low temperature zone and the high temperature zone; and the comparison step is executed again. If the preset number of times is reached, the control process of the temperature control zone is executed; if the preset number of times is not reached, the following steps are executed: when the actual temperature is currently in the high temperature zone, the total duty cycle calculation step and the duty cycle determination step are skipped, the heating element 2 is controlled to execute the duty cycle corresponding to the high temperature zone, and the temperature detection step in the cavity is returned; when the actual temperature is currently in the low temperature zone, the total duty cycle calculation step and the duty cycle determination step are skipped, the multiple heating elements 2 are controlled to execute the duty cycle corresponding to the low temperature zone, and the temperature detection step in the cavity is returned.

[0063] The above judgment steps also include the judgment result that the actual temperature is currently in the temperature control zone. When the current temperature is in the temperature control zone, the control process of the temperature control zone is executed.

[0064] The control process of the temperature control zone includes: a total duty cycle calculation step, which calculates the total duty cycle based on the actual temperature and the target temperature; and a duty cycle determination step, which determines the duty cycle corresponding to each switching element 3 based on the total duty cycle and the preset proportional relationship.

[0065] In some implementations, after controlling each heating element 2 to operate according to the corresponding duty cycle, the process further includes: recording the temperature zone where the current actual temperature is located, so that in the above judgment step, the current temperature zone is compared with the previous temperature zone, thereby improving the accuracy of the judgment.

[0066] In a preferred embodiment of the present invention, the step between calculating the total duty cycle and determining the duty cycle further includes:

[0067] Limiting Step: After calculating the total duty cycle, determine the output total duty cycle based on its relationship with the first duty cycle threshold and the second duty cycle threshold. Specifically, if the total duty cycle is less than the first duty cycle threshold, output the first duty cycle threshold; if the total duty cycle is greater than the second duty cycle threshold, output the second duty cycle threshold; if the total duty cycle threshold is between the first and second duty cycle thresholds, output the total duty cycle obtained in the total duty cycle calculation step.

[0068] Therefore, based on the total duty cycle after the limit and the preset relationship, the further step also includes determining the duty cycle corresponding to each switching element 3 based on the preset relationship and the total duty cycle of the output, thereby controlling each heating element 2 to operate according to the corresponding duty cycle.

[0069] In a preferred embodiment of the present invention, a preset step is further included: presetting a preset relationship between the duty cycle of each switching element and the total duty cycle; the preset step can be performed before calling the preset relationship, and this embodiment does not specifically limit it. Preferably, the preset proportional relationship between the duty cycle of each switching element 3 and the total duty cycle is: an = kn * a, where a1, a2...an are the duty cycles of each switching element 3; a is the total duty cycle; and k1, k2...kn are proportional coefficients. By proportionally distributing the duty cycle to multiple switching elements to adjust the temperature inside the food cooking device, the temperature uniformity inside the food cooking device can be improved, and the defects of frequent replacement of heating element 2 due to the shortened lifespan of heating element 2 caused by using a single specific heating element 2 can be avoided, thus extending the service life of the food cooking device.

[0070] Preferably, the proportionality coefficient is the dependent variable of the target temperature. Different target temperatures result in different proportionality coefficients for the same heating element 2. By adjusting the proportionality coefficient according to the different target temperatures, the temperature distribution within the food preparation apparatus can be improved, thereby enhancing the quality of food preparation.

[0071] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A food preparation apparatus, comprising: A chamber used to hold food to be prepared; Multiple heating elements are arranged corresponding to the chamber and used to heat the chamber; Multiple switching elements are connected to multiple heating elements respectively, so as to adjust the output of multiple heating elements by adjusting the duty cycle; A temperature sensing element is used to detect the actual temperature inside the cavity; A controller is used to set the target temperature of the chamber; The controller is characterized in that it is configured to execute: The total duty cycle calculation steps involve calculating the total duty cycle based on the actual temperature and the target temperature. The duty cycle determination step involves determining the duty cycle corresponding to each of the switching elements based on the total duty cycle and a preset proportional relationship. The controller is further configured to: determine whether the difference between the actual temperature and the target temperature is within a specified temperature difference range, the specified temperature difference range including a low-temperature zone, a temperature-controlled zone, and a high-temperature zone, the temperature range of the temperature-controlled zone being between the low-temperature zone and the high-temperature zone; if the difference is within the low-temperature zone or the high-temperature zone, skip the total duty cycle calculation step and the duty cycle determination step; if the difference is within the temperature-controlled zone, execute the total duty cycle calculation step and the duty cycle determination step. Furthermore, the controller is configured to execute: a judgment step, determining whether the temperature zone currently occupied by the actual temperature and the temperature zone previously occupied are respectively the low temperature zone and the high temperature zone, or respectively the high temperature zone and the low temperature zone; if so, counting it as one switch between the low temperature zone and the high temperature zone; a recording step, recording the number of switches of the actual temperature between the low temperature zone and the high temperature zone; a comparison step, comparing the number of switches with a preset number; if the number of switches is not less than the preset number, then executing the total duty cycle calculation step and the duty cycle determination step.

2. The food preparation apparatus according to claim 1, characterized in that, The preset ratio between the duty cycle of each of the aforementioned switching elements and the total duty cycle is: an = kn a, where, a1, a2…an are the duty cycles of each of the aforementioned switching elements; 'a' represents the total duty cycle; k1, k2…kn are proportionality coefficients.

3. The food preparation apparatus according to claim 2, characterized in that, The proportionality coefficient is the dependent variable of the target temperature.

4. The food preparation apparatus according to claim 1, characterized in that, The switching element is a relay, and the relay has a working cycle of 10-30 seconds.

5. The food preparation apparatus according to claim 1, characterized in that, The switching element is a solid-state relay or a silicon controlled rectifier (SCR).

6. A method for temperature control of a food preparation apparatus, the food preparation apparatus comprising: A chamber used to hold food to be prepared; Multiple heating elements are arranged corresponding to the chamber and used to heat the chamber; Multiple switching elements are connected to multiple heating elements respectively, so as to adjust the output of multiple heating elements by adjusting the duty cycle; A temperature sensing element is used to detect the actual temperature inside the cavity; A controller is used to set the target temperature of the chamber; The temperature control method is characterized by comprising the following steps: The total duty cycle calculation steps involve calculating the total duty cycle based on the actual temperature and the target temperature. The duty cycle determination step involves determining the duty cycle corresponding to each of the switching elements based on the total duty cycle and a preset proportional relationship. Determine whether the difference between the actual temperature and the target temperature is within a specified temperature difference range. The specified temperature difference range includes a low-temperature zone, a temperature-controlled zone, and a high-temperature zone. The temperature range of the temperature-controlled zone is located between the low-temperature zone and the high-temperature zone. If the difference is within the low-temperature zone or the high-temperature zone, skip the total duty cycle calculation step and the duty cycle determination step. If the difference is within the temperature-controlled zone, execute the total duty cycle calculation step and the duty cycle determination step. The temperature control method further includes the following steps: The judgment step is to determine whether the temperature zone where the actual temperature is currently located and the temperature zone where it was located in the previous temperature are respectively the low temperature zone and the high temperature zone, or the high temperature zone and the low temperature zone. If so, it is counted as a switch between the low temperature zone and the high temperature zone. Record the steps, including the number of times the actual temperature switches between the low-temperature zone and the high-temperature zone; The comparison step compares the number of switching operations with the preset number of switching operations; if the number of switching operations is not less than the preset number of switching operations, then the total duty cycle calculation step and the duty cycle determination step are executed.

7. The temperature control method for the food preparation apparatus according to claim 6, characterized in that, The preset ratio between the duty cycle of each of the aforementioned switching elements and the total duty cycle is: an = kn a, where, a1, a2…an are the duty cycles of each of the aforementioned switching elements; 'a' represents the total duty cycle; k1, k2…kn are proportionality coefficients.

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